Anthropogenic Influences on the African Easterly Jet-African Easterly Wave System

The African easterly jet (AEJ)-African easterly wave (AEW) system is a central feature of the summertime circulation over North Africa. Despite their North African home of origin, AEWs can have far-reaching effects as they often play an important role in tropical cyclone development. While there has been extensive research on AEWs, the response of AEWs to the changing climate is less understood. In this study, we use the Weather Research and Forecasting (WRF) model configured as a tropical channel model (spanning approximately 30S - 50N) to examine AEW behavior. For our control experiment, we choose July-September (JAS) of 2017 as this was an active hurricane season with several hurricanes originating from AEWs. The control simulation is an ensemble of WRF hindcasts of JAS 2017 forced by the historical sea-surface temperatures (SSTs) and north/south lateral boundary conditions as they actually occurred. To examine AEWs in a changing climate, we repeat the JAS 2017 WRF simulation by perturbing the model to pre-industrial and future mean climate states, while retaining the same interannual SST variability as 2017. Comparison of these WRF simulations will provide new insight into how the AEJ-AEW system has responded to the changing climate. We begin our analysis by looking at the temperature gradient over North Africa, the SST gradients within the tropical Atlantic and between the Atlantic and Pacific, the precipitation related to the West African monsoon, and the location and magnitude of the AEJ. We then consider the response of the AEWs by evaluating the frequency, location, and strength of the waves. The eddy kinetic energy and the baroclinic and barotropic energy conversions are calculated to assess the strength of the AEWs and their relationship to the AEJ.